Projection transparency having
a transparent powder image



Nov. 28, 1967 L. E. WALKUP 3,355,308

1 PROJECTION TRANSPARENCY HAVING A TRANS-PARENT POWDER IMAGE Original Filed June 24, 1963 2 Sheets-Sheet 1 FIG. 1 IN i as a:

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4, W as 44 A A l A l (4? T T INVENTOR. 5 LEWIS LKUP United States Patent 3,355,308 PRGJECTION TRANSPARENCY HAVING A TRANSPARENT POWDER IMAGE Lewis E. Walkup, Columbus, Ohio, assignor, by mesne assignments, to Xerox Corporation, Rochester, N.Y., a corporation of New York Original application June 24, 1963, Ser. No. 289,904, now Patent No. 3,196,765. Divided and this application Dec. 24, 1964, Ser. No. 42i),87tl

3 Qiaims. (Cl. 117-9) This application is a division of my copending application Ser. No. 289,904, led June 24, 1963, now Patent No. 3,196,765.

This invention relates to xerography, in general, and to the development and display of images, in particular.

Xerography has become a well-known process for producing copies of printed matter, pictures, writings, and other scenes. Typically, a xerographic copy comprises a powder image of pigmented resin, or toner, on a support base such as paper, plastics, and the like. Depending upon the particular application, the support base will be transparent, translucent or opaque, and the toner image viewed by transmitted or reflected light.

Suitability of a xerographic copy is generally related to the density of the toner image. For instance, a black toner image on white paper must absorb sufiicient light to be readable. Similarly, a xerographically produced transparency must be sufliciently dense to block light projected through it so that the image may be viewed on a projection screen or other imaging surface.

Because the toner is selectively attracted to the support base by electrostatic forces, it is sometimes difficult to achieve sutficient image density especially when the image is made up of very fine lines. If too little toner is attracted, the copy, or a projection of it, will be lacking in contrast, or even totally unreadable. Hence, imaging independent of toner density is a highly useful contribution to the art.

Accordingly, a new and improved method of xerographic imaging independent of toner density is an object of this invention.

A novel xerographic transparency and method for making it are also objects of this invention.

Other objects of this invention include: high resolution image projection; high contrast image projection; the application of xerography to reduced size image pr0jection; quick display of optical images, and novel apparatus therefore.

As explained in detail below, the present invention requires the use of xerographic toner and image support bases having specially selected properties. An especially suitable support base comprises normally transparent material having a light scattering surface. According to one embodiment of the present invention, a toner image is formed on a xerographic plate and transferred, after a tackifying step, to the light scattering surface of a support base. The transferred toner image is then processed to render the light scattering surface selectively transparent. Although the present invention may be used for making copies directly viewable by reflected light, its probably greater value resides in slides or transparencies viewable by projection. These and other embodiments of the present invention are described in detail in connection with the drawing in which:

FIG. 1 illustrates a light scattering member;

FIG. 2A and FIG. 2B illustrate the process of making the light scattering member selectively transparent;

FIG. 3 illustrates image projection;

FIG. 4 illustrates electrostatic transfer of a xerographic toner image;

FIG. 5 illustrates apparatus and method for continuous reproduction of images; and,

FIG. 6 illustrates an image web for use in the present invention.

FIG. 1 illustrates support base 10 made of glass, clear plastic or other normally transparent material. One surface of support base 10 must be sufficiently frost-like or reticulated to be substantially light scattering, and such surface is shown in FIG. 1 as image surface 11. A suitable support base, therefore, may comprise ground glass, ground plastic, frosted polyethylene films, and the like. Image surface 11 is preferably sufliciently light diffusing such that if used in a stereopticon or slide projector support base 10 would allow only a small portion of the collimated light directed toward it to reach the viewing screen. Thus, the image areas of surface 11 focused on a viewing screen by the objective lens would appear nearly black.

FIG. 2A illustrates the first step in rendering support base 10 selectively transparent according to the present invention. Image surface 11 is shown in contact with xerographic plate 15 on which has been formed toner image 12. Toner image 12 conforms to a document or other original scene, and is formed by any one of a number of methods Well-known to the art of xerography. For instance, according to one well-known method, xerographic plate 15 comprising a photoconductive layer 16 overlying conductive backing 17 is uniformly charged in darkness by means :of a corona discharge device. Exposure to a pattern of light and shadow selectively discharges the plate and forms a latent electrostatic image. The latent electrostatic image is made visible as toner image 12 by dusting photoconductive layer 16 with finely divided electrically charged resin powder particles. Usually, the powder particles are charged to a polarity opposite to that of the latent electrostatic image so that the particles are attracted by, and adhere to, charged areas of plate 15. However, if desired for a particular application, like rather than opposite polarities may be selected so that the powder particles will be attracted to the discharged areas of plate 15 instead. Other xerographic techniques may be used in place of the one described as the particular method of forming toner image 12 does not constitute a part of this invention.

To facilitate transfer of toner image 12 to image surface 11 of support base 10, powder image 12 is made more tacky or adhesive. This may be done by heating powder image 12, or more desirably, by exposing powder image 12 to the vapors of a volatile liquid which act as a solvent for the resinous material.

Tackifying toner image 12 with solvent vapor is illustrated by FIG. 2B. Support base 15 bearing toner image 12 may be immersed in solvent vapor 18 contained in vapor chamber 19. Although the particular volatile liquid used will depend upon the constituency of toner image 12, it can generally be stated that suitable solvents include, but are in no way limited to, chloroform, carbon tetrachloride, trichloroethylene and other chlorinated solvents. Aromatic and aliphatic hydrocarbons such as benzene, toluene, gasoline and gasoline fractions, and other alcohols and oxygenated solvents may be used.

Image surface 11 of support base 10 is simply placed in contact with the tackified image under mild pressure, for example, by pressing with the hands. Plate 15 and support base 10 are then separated and sufficient toner will adhere to image surface 11 for purposes of the present invention.

It has been found that support base 10 with toner image 12 on its image surface 11 comprises an image member which may be used as a slide or transparency in a stereopicon, slide projector or other similar viewing device.

FIG. 3 illustrates one use of an image member made in accordance with the present invention. Converging beam 21, produced from light source 22 by condensing.

system 25, illuminates image surface 11 of support base 10. Objective lens 23 is positioned to focus image surface 11 in an image plane, such as viewing screen 24. Since image surface 11 is transparent in areas of toner image 12, light is transmitted in image configuration and appears on projection screen 24. The non-image areas of image surface 11 remain light scattering and light directed thereon is essentially lost from the optical system. Thus, there is caused to appear on screen 24 a bright display, corresponding to toner image 12, on a dark background.

As used in the present invention, toner image 12 comprises a transparent resin or other material which may be softened by heat, vapor solvent, or other controllable element. If desired, the toner material may be dyed. Image contrast is enhanced by using a toner image 12 of nearly the same index of refraction as that of support base 19 although readable images may also be made with other images. Commercially available nonpigmented xerogrphic toners have been successfully used in the present invention.

FIG. 4 illustrates an alternative method for transferring toner image 12 to image surface 11. This embodiment dispenses with the transfer softening step described in connection with FIG. 2.

Image surface 11 is again shown in contact with xerographic plate 15 hearing toner image 12. An electrostatic charge opposite in polarity to that of toner image 12 is applied to the non-diffusing surface 13 of support base 10 by means of charging device 26. Any suitable charging device known to the art of xerography may be used, and the one schematically represented in FIG. 4 comprises conductive strand 27 partly surrounded by grounded shield 28. Conductive strand 27 is raised to a high potential by means of power supply 29 resulting in the uniform charging of surface 13 through slit 30 as charging device 26 is moved in the direction shown by the arrow. Other suitable devices are described, for example in US. Patents 2,777,- 957 and 2,836,725. Whatever charging method is employed, or whatever other transfer technique is employed, it is only necessary that the attraction of toner image 12 for photoconductive layer 16 be overcome and toner image 12 transferred to image surface 11 of support base 10.

Atlhough carrying out the steps just described in connection with FIG. 4 will produce an image member suitable for projection purposes, it has been found that an additional fusing step results in a superior slide or transparency. Fusing of the transferred toner image 12 may be accomplished in the manner of transfer softening described in connection with FIG. 2B. It is believed that the fusing step causes the powder comprising toner image 12 to fill in the tiny pockets of image surface 11 thereby removing the diffusing property of those areas and rendering them highly transparent. Image members having fused toner images have been found to produce projection images that are of higher contrast and much brighter than images produced by image members having non-fused toner images.

FIG. illustrates an embodiment for the continuous production of transparencies according to the present invention. Although this embodiment incorporates an electrostatic frosting process to form the light diffusing surface of the transparency, it should be noted that the frosting process may be dispensed with when a pre-frosted image web 32 is used.

To fully describe the present invention, reference is first made to FIG. 6 which more clearly illustrates the composition of image web 32. As shown, web 32 comprises a photoconductive deformable layer 33 overlying support layer 34. Both layers are necessarily flexible and transparent. A thin transparent conductive layer 35 need be incorporated into the structure only if support layer 34 is electrically non-conductive.

Specifically, a highly suitable web 32 may comprise a support layer 34 of Mylar polyester film (E. I. du Pont de Nemours & Co.), copper iodide layer 35, and a photoconductive deformable layer 33 of a photoconductor corresponding to Formula 2 of Canadian Patent No. 568,707 mixed with Staybelite 10 (Hercules Powder Company).

Referring to FIG. 5, image web 32 is fed from supply roll 37 through various process stations.

A light diffusing surface is first imported to web 32 in the manner fully described in copending patent application Ser. No. 193,277, now Patent No. 3,196,011. Successive portions of web 32 are electrostatically charged in the absence of light by means of corona charging device 38 which is connected to high voltage power supply 39. Deformable layer 33 is next softened so that it becomes physically altered by the mechanical force associated with the electrical field existing across layer 33 as a result of the aforementioned charging. Softening is most commonly done by exposing web 32 to an atmosphere of solvent vapors for the materials of layer 33, or by heating as illustrated in FIG. 5. Heating element 53 is shown positioned below web 32. As the material of layer 33 is softened it is enabled to flow in response to the electrostatic forces acting upon it, and the softened layer 33 develops a microscopically uneven surface having a frosted appearance. This surface is sufficiently light diffusing for use in the present invention. It is referred to as image surface 40 in connection with the remaining steps shown in FIG. 5.

Successive portions of web 32 are again electrostatically charged in the absence of light, as schematically represented by charging device 41 connected to high voltage power supply 42.

Web 32 is then exposed to a light and shadow pattern of a document 43, or other original, for example, by projection of reflected light 44 from lamp 45 through lens 46. Since layer 33 is photoconductive, exposure causes selective dissipation of the electrostatic charge leaving a latent electrostatic image which may be developed or made visible at xerographic developing stattion 50.

The developing method known in the art of xerography as cascade development is highly suitable for the present invention and is fully described in US. Patents 2,618,551; 2,618,552; and 2,638,416. A mixture of tiny electrically charged resin toner particles and grossly larger carrier material is cascaded or poured across image surface 40 of web 32. Powder cloud developement or liquid development, as known to the art, are also useful developing systems depending on the image being formed. According to the illustrated embodiment, the resin particles are attracted by and adhere to the charged areas of image web 32 forming toner image 51.

In a manner similar to that explained in connection with FIGS. 2 and 4, toner image 51 is appropriately softened to create an intimate bond between individual particles and with image surface 40. As illustrated in FIG. 5, image web 32 passes through focusing chamber 55 in which it is exposed to an atmosphere to solvent vapors for toner image 51. Thus rendered selectively transparent in image configuration, image web 32 is suitable for use as a transparency for the projection display of the image thereon. After it leaves fusing chamber 55, image web 32 may be stored for later use as on roller 67, or it may pass through viewing station 60 for quick projection display as illustrated in FIG. 5. At viewing station 60 image surface 40 is illuminated by convergent beam 61 produced from light source 63 by condensing system 62. Light is freely transmitted by the transparent or image areas of image surface 40 but is nearly completely blocked by diffusion as the non-transparent or non-image areas. There results a high contrast projected image on screen 64.

Various modifications and adaptations of the present invention are within the capability of those skilled in the art. Therefore, it is intended that the following claims be interpreted broadly to cover all embodiments of the present invention as well as the specific embodiments illustrated herein.

What is claimed is:

1. A projection transparency comprising:

(a) a support member of normally transparent material having a light diffusing surface; and

(b) a transparent powder image on said surface.

2. A projection slide comprising:

(a) a support member or normally transparent material having a reticulated light-scattering surface; and,

(b) a transparent fused powder image on said surface.

3. A projection slide according to claim 2 in which said powder image and said support member have substantially the same indexes of refraction.

References Cited UNITED STATES PATENTS 584,107 6/1897 Brown 1611 789,697 5/1905 Kyle 161--5 874,885 12/1907 Dodge 161-1 1,580,921 4/1926 Scherer 1179 1,973,792 11/1930 Barrows 1611 2,362,980 9/1941 Ball 16l6 2,386,626 10/1945 Nadeau et a1. 11'729 2,545,896 1/1948 Pipkin 117-18 2,682,478 6/1954 Howsc 11723 2,719,098 9/1955 Goldman 881 2,818,354 12/1957 Pritikin et a1. 117-159 3,108,895 10/1963 Howell et a1. 11717.5 X 3,113,179 12/1963 Glenn 117-17.5 X 3,147,136 9/1964 Huttenbach et a1. 1l7159 864,387 8/1907 Pfister 11723 X 2,444,863 7/1948 Tornberg 11713 2,681,473 6/1954 Carlson 11717.5 X 2,992,937 7/1961 Davis 117-13 3,241,957 3/1966 Fauser et a1. 1l737 X WILLIAM D. MARTIN, Primary Examiner.

Assistant Examiners. 

1. A PROJECTION TRANSPARENCY COMPRISING: (A) A SUPPORT MEMBER OF NORMALLY TRANSPARENT MATERIAL HAIVNG A LIGHT DIFFUSING SURFACE; AND (B) A TRANSPARENT POWDER RINGS ON SAID SURFACE. 